Invalid Signature - HELP

I spend most of my day adjusting my app to the 2.0 version. My Problem is that I can successfully connect to Facebook but all following requests fail due to an "Invalid Signature" error. This probably means that there is some diversity in the way
the signature string is build or hashed.
This call initital call works:URL: https://api.facebook.com/bestserver.phpPOST: method=facebook.auth.getSession&auth_token=784cb7274d3ebaaf5f9b8c5dca52cef7&session_key=&api_key=MYAPIKEY&v=1.0&call_id=8cac775abc2afe0&sig=014780ea0c4789b7ff817e1cededab74

This is what gets generated on the next call (getInfo):URL: https://api.facebook.com/bestserver.phpPOST: method=facebook.users.getInfo&uids=SOMEUSERID&fields=first_name%2c+last_name%2c+name%2c+pic_small%2c+pic_big%2c+pic_square%2c+pic%2c+affiliations%2c+profile_update_time%2c+timezone%2c+religion%2c+birthday%2c+sex%2c+hometown_location%2c+meeting_sex%2c+meeting_for%2c+relationship_status%2c+significant_other_id%2c+political%2c+current_location%2c+activities%2c+interests%2c+is_app_user%2c+music%2c+tv%2c+movies%2c+books%2c+quotes%2c+about_me%2c+hs_info%2c+education_history%2c+work_history%2c+notes_count%2c+wall_count%2c+status&session_key=f64b3e311419540323c6eb41-597334294&api_key=MYAPIKEY&v=1.0&call_id=8cac775e5264e90&sig=f43a8e7f62f6397f7c200d3684256538

The call returns with an incorrect signature XML response...

This what I use for testing (and what used to work with the old API:
public override bool Connect()
{
var fs = new facebook.Components.FacebookService();
fs.ApplicationKey = VendorAppID;
fs.Secret = VendorSecret;

I initially set up facebook.Components.Service and then reuse it (store it in the app memory) on subsequent requests.
What seems to be happening is that the Service "looses" it´s AppSecret key and because of that it produces an invalid signature.

The exact same source code worked (still does work) pretty well with the old version. Any hints on why this is happening?

Have you been able to successfully build the source? Do you have Linq2XSD installed?
Building and using the
modified source works quite well for me (apart from not being able to post profile messages).